1. Field of the Invention
This invention relates to glazing panels and particularly, but not exclusively, to solar control glazing panels which are intended to undergo heat treatment following application of a solar control filter.
2. Discussion of Background
EP 233003 A describes a glazing panel carrying a sputter coated optical filter having the structure: glass substrate/SnO2 base dielectric/first metallic barrier of Al, Ti, Zn, Zr or Ta/Ag/second metallic barrier of Al, Ti, Zn, Zr or Ta/SnO2 top dielectric. The optical filter is designed to block a significant portion of the incident radiation in the infra red portion of the spectrum whilst allowing passage of a significant portion of the incident radiation in the visible portion of the spectrum. In this way, the filter acts to reduce the heating effect of incident sunlight whilst allowing good visibility through the glazing and is particularly suitable for car windscreens.
In this type of structure, the Ag layer acts to reflect incident infra red radiation and in order to fulfil this role must be maintained as silver metal rather than silver oxide and must not be contaminated by adjacent layers. The dielectric layers which sandwich the Ag layer serve to reduce the reflection of the visible portion of the spectrum which the Ag layer would otherwise provoke. The second barrier serves to prevent oxidation of the Ag layer during sputtering of the overlying SnO2 dielectric layer in an oxidising atmosphere; this barrier is at least partially oxidised during this process. The main role of the first barrier is to prevent oxidation of the silver layer during heat treatment of the coating (e.g. during bending and/or tempering) of the glazing panel by being oxidised itself rather than allowing passage of oxygen to the Ag layer. This oxidation of the barrier during heat treatment provokes an increase in TL of the glazing panel.
EP 792847A discloses a heat treatable solar control glazing panel which is based on the same principle and has the structure: glass substrate/ZnO dielectric/Zn barrier/Ag/Zn barrier/ZnO dielectric/Zn barrier/Ag/Zn barrier/ZnO dielectric. The Zn barriers positioned below each of the Ag layers are intended to be oxidised completely during heat treatment and serve to protect the Ag layers from oxidation. As well known in the art, the structure of having two, spaced Ag layers rather than a single layer Ag layer increases the selectivity of the filter.
EP 718250A discloses the use of a layer which provides a barrier to oxygen diffusion as at least part of the outermost dielectric layer in this type of filter stack. Such a layer must have a thickness of at least 100 xc3x85 and preferably at least 200 xc3x85 in order to form an effective barrier and may comprise a silicon compound SiO2, SiOxCy, SiOxNy, nitrides like Si3N4 or AlN, carbides like SiC, TiC, CrC and TaC.
The antireflective layer is a layer composed of at least one member selected from the group consisting of oxides, nitrides and carbides and double compounds thereof.
As the oxide, for example, an oxide of at least one element selected from the group consisting of Zn, Ti, Sn, Si, Al, Ta or Zr may be mentioned. In addition, for example, zinc oxide containing Al, Ga, Si or Sn or indium oxide containing Sn may be mentioned.
As the nitride, a nitride of at least one element selected from the group consisting of Si, Al and B (a nitride (A)) or a mixture (inclusive of a double nitride) of a nitride of Zr or Ti with a nitride (A) may be mentioned.
As the double compound, SiOxCy, SiOxNy, SiAlxNy or SiAlxOyNz may be mentioned. The antireflective layer may be a single layer or a multiple layer.
Especially, a zinc oxide or a zinc oxide containing at least one element selected from the group consisting of Sn, Al, Cr, Ti, Si, B, Mg, In and Ga is preferable, because it makes it possible to stably form an adjacent infra-red reflecting layer with a high crystallinity. Especially, a zinc oxide containing Al and/or Ti is preferable.
The infra-red reflecting material is a material that has a reflectance higher than the reflectance of sodalime glass in the band of wavelength between 780 nm and 50 xcexcm.
The infra-red reflecting layer is a layer composed of Ag only or a layer comprising Ag as the main component and an additional metal element (such as Pd, Au or Cu). When an additional metal element is contained, the content of the additional metal element is preferably from 0.3 to 10 at %, more preferably from 0.3 to 5 at %, based on the total of Ag and the additional metal element. If the content of an additional metal element is less than 0.3 at %, the effect of stabilizing Ag is small. Also, if the content of an additional metal element exceeds 10 at %, the effect of stabilizing Ag diminishes. Especially, Pd as the additional metal element can immobilize Ag atoms, namely depress the migration of Ag atoms and affords a layer which is excellent in stability and chemical resistance at high temperatures. As the Pd content increases, the rate of film formation tends to decrease, the visible light transmittance tends to lower, and the shielding selectivity between visible rays and near infrared rays tends to become poor. Therefore, the Pd content (Pd/Ag) is preferred to be at most 5.0 at %, especially from 0.3 to 2.0 at %, more preferably from 0.3 to 1.0 at %.
When the glass laminate of the present invention comprises more than one infra-red reflecting layer, each infra-red layer may have the same composition or a different composition. The infra-red reflecting layer may be a multiple layer comprising at least two laminated films, for example, a multiple layer composed of Ag and Pd.
In a glazing panel having a three layer type laminated coating, the thickness of the base antireflective layer, the infra-red layer and the top antireflective layer layer are preferably from 15 to 45 nm, from 9 to 16 nm (especially from 9 to 12 nm) and from 30 to 45 nm, respectively. A glazing panel comprising a colorless soda lime glass substrate of 2 mm thick and a three layer type laminated coating formed on the substrate has such representative optical properties as a luminous transmittance (TL) of about from 75 to 85% and an energetic transmittance (TE) of about from 50 to 70% after heat treatment.
In a glazing panel having a five layer type laminated coating, the thicknesses of the base antireflective layer, the infra-red layer the central antireflective layer, the infra-red layer and the top antireflective layer layer are preferably from 16 to 50 nm (especially from 20 to 45 nm), from 6.5 to 16 nm (especially from 6.5 to 12.5 nm), from 40 to 100 nm (especially from 45 to 90 nm), from 6.5 to 16 nm (especially from 6.5 to 12.5 nm) and from 16 to 50 nm (especially from 20 to 45 nm), respectively. A glazing panel comprising a colorless soda lime glass substrate of 2 mm thick and a five layer type laminated coating formed on the substrate has such representative optical properties as a luminous transmittance (TL) of about from 70 to 80% and an energetic transmittance (TE) of about from 40 to 50% after heat treatment.
The term xe2x80x9cheat treatable glazing panelxe2x80x9d as used herein means that the glazing panel carrying the coating stack is adapted to undergo a bending and/or thermal tempering and/or thermal hardening operation and/or other heat treatment process without the haze of the so treated glazing panel exceeding 0.5, and preferably without the haze exceeding 0.3. The term xe2x80x9csubstantially haze free heat treated glazing panelxe2x80x9d as used herein means a glazing panel carrying a coating stack which has been bent and/or thermally tempered and/or thermally hardened and has a haze that does not exceed 0.5 and which preferably does not exceed 0.3. In the present invention, a glazing panel can be subjected to heat treatment for 1) bending, 2) tempering, 3) sintering of colored ceramic print or silver bus bar print, 4) vacuum sealing of vacuum double glazing and 5) calcination of a wet-coated low reflective coating or antiglare coating. For example, it is heated to a temperature of from 570 to 700xc2x0 C. in the atmosphere for 1) bending or 2) tempering. The bending and/or thermal tempering and/or thermal hardening operation may be carried out at a temperature of at least, 600xc2x0 C. for at least 10 minutes, 12 minutes, or 15 minutes, at least 620xc2x0 C. for at least 10 minutes, 12 minutes, or 15 minutes, or at least 640xc2x0 C. for at least 10 minutes, 12 minutes, or 15 minutes.
Any suitable method or combination of methods may be used to deposit the coating layers. For example, evaporation (thermal or electron beam), liquid pyrolysis, chemical vapour deposition, vacuum deposition and sputtering, particularly magnetron sputtering, the latter being particularly preferred. Different layers of the coating stack may be deposited using different techniques.
The nitride of aluminium may be pure AlN, substantially pure AlN, AlN containing impurities or AlN containing one or more dopants, for example, chromium and/or silicon and/or titanium, which may improve chemical durability of the material. The nitride of aluminium may contain about 97% pure AlN by weight. Alternatively, it may contain an oxynitride, a carbonitride or an oxycarbonitride. The nitride of aluminium may be deposited by sputtering a target in a nitrogen atmosphere. Alternatively, it may be deposited by sputtering a target in an atmosphere which is a mixture of argon and nitrogen.
The target may be 6061 alloy, 6066 alloy, 4032 alloy, etc.
A nitride of aluminium in the base antireflective layer is believed effective in blocking not only oxygen but also sodium ions and other ions that can diffuse from the glass into the coating stack and cause a deterioration of optical and electrical properties, particularly if the glazing panel is subjected to heat treatment.
SiO2 and Al2O3 are known to be effective barriers to diffusion of sodium ions in sputtered coating stacks. In addition to being easier, quicker and more cost effective to deposit by sputtering, it is believed that a nitride of aluminium as part of the base dielectric layer provides an effective barrier to both sodium ions and oxygen diffusion. Furthermore, it is believed that a nitride of aluminium may provide an effective diffusion barrier at smaller geometrical thicknesses than that required using known materials. For example, good thermal resistance with respect to ion and oxygen diffusion from the glass substrate may be conferred on the coating stack by arranging a nitride of aluminium having a geometrical thickness of greater than 40 xc3x85, for example, about 50 xc3x85 as at least part of the base antireflective layer particularly if the coating stack also includes a barrier layer, for example a metal or sub-oxide barrier layer, underlying the infrared reflecting layer. In the absence of such a barrier layer underlying the infra-red reflecting layer, good thermal resistance with respect to ion and oxygen diffusion from the glass substrate may be conferred on the coating stack by arranging a nitride of aluminium having a geometrical thickness of greater than 50 xc3x85, preferably greater than 80 xc3x85 or 90 xc3x85, for example, about 100 xc3x85 as at least part of the base antireflective layer. A layer of a nitride of aluminium may confer advantageous properties even if it is less than 195 xc3x85 thick.
The coating stack may comprise a barrier layer overlying the infra red reflecting layer and/or a barrier layer underlying the infra red reflecting layer. Such barriers may contain one or more metals and may be deposited, for example, as metal oxides, as metal sub-oxides or as metals.
Further, in the invention, when a layer composed of an oxide or a double compound containing an oxide such as an oxynitride is formed as an antireflective layer by reactive sputtering in an atmosphere containing an oxidative gas, formation of such antireflective layer directly on the infra-red reflecting layer can fail to give a glazing panel having desired optical and electrical properties because of oxidation of the infra-red reflecting layer Therefore, it is preferred to form a metal or nitride barrier layer. Such a barrier layer usually stays in a partly oxidized state, and during heat treatment, oxidizes into a transparent oxide having a higher visible light transmittance.
As the barrier layer, a metal of at least one element selected from the group consisting of Ti, Zn, Alxe2x80x94Zn, Tixe2x80x94Zn, SUS, Zr, Ta, NiCr, Ni, Nixe2x80x94Ti, a nitride of at least one element selected from the group consisting of Ti, Zn, Alxe2x80x94Zn, Tixe2x80x94Zn, SUS, Zr, Ta, NiCr, Ni, Nixe2x80x94Ti, and a sub-oxide (i.e. partially oxized) of at least one element selected from the group consisting of Ti, Zn, Alxe2x80x94Zn, Tixe2x80x94Zn, SUS, Zr, Ta, NiCr, Ni, Nixe2x80x94Ti is preferable. The thickness of a barrier layer is preferably from 1 to 5 nm. A barrier layer thinner than 1 nm does not work well, while a barrier layer thicker than 5 nm can lower the visible light transmittance of the glass laminate or cause other problems.
When an oxide layer, for example, composed of zinc oxide containing Al is formed directly on the infra-red reflecting layer as the antireflective layer, an Alxe2x80x94Zn alloy barrier layer having the same metal ratio can strengthen the adhesion between the infra-red reflecting layer and the antireflective layer and thus is effective in improving durability of the layers of the multilayer structure. An Alxe2x80x94Zn alloy barrier layer is also preferable in view of the crystallinity of Ag in the infra-red reflecting layer and the heat resistance. A barrier layer may be formed under the infra-red reflecting layer, too.
The ability to block ion and oxygen diffusion from the glass substrate with a relatively thin layer provides great flexibility in the materials and thickness that may be used for the other layers in the coating stack.
Providing a layer of a metal oxide between the nitride of aluminium and the infra-red reflecting material (particularly when this is silver or a silver alloy) may combine the thermal stability properties of the nitride of aluminium with an interposed material which favours crystallisation of the infra-red reflecting material so as to balance the infra red reflecting properties with the haze of the coating stack, particularly when it is subjected to heat treatment. One preferred such oxide is a mixed oxide of zinc and aluminium, preferably with a Al/Zn atomic ratio of about 0.1-0.2, especially 0.1-0.15. One possible explanation for this may be that the presence of the Al in the zinc oxide structure may reduce the crystal grain growth in the mixed oxide layer.
The effectiveness of a relatively thin layer of the nitride of aluminium in conferring thermal stability allows use of a relatively thick layer of such an oxide.
Both Si3N4 and AlN take longer to deposit by common sputtering techniques than oxides traditionally used in such coatings e.g. ZnO, SnO2. The ability to provide good thermal stability with a relatively thin layer of a nitride of aluminium thus alleviates the deposition of such a layer as a limiting factor in a deposition process.
A nitride of aluminium is also more cost effective to deposit by sputtering than, for example, Si3N4 and does not require the doping or control precautions required for depositing Si3N4.
The optical thickness of the antireflective layers and particularly that of the top antireflective layer is critical in determining the colour of the glazing panel. If a portion of an antireflective layer is oxidised, for example during heat treatment of the glazing panel then, particularly with Si3N4 (refractive index about 2) the optical thickness can be modified as Si3N4 may be oxidised to SiO2 (refractive index about 1.45). Where the antireflective layer comprises a nitride of aluminium having a refractive index of about 2.0, oxidation of a part of this to Al2O3 (refractive index about 1.7) will have negligible effect upon the optical thickness of the layer.
The ability to use a layer of a nitride of aluminium which is less than 100 xc3x85 in thickness to provide an effective thermal barrier provides significant flexibility in the choice of the overall structure of the top antireflective layer. The layer comprising a nitride of aluminium may be about 85 xc3x85 in thickness; this provides a compromise between good thermal resistance and thickness. The layer comprising a nitride of aluminium may have a geometrical thickness of greater than or equal to about 50 xc3x85, 60 xc3x85 or 80 xc3x85; its thickness may be less than or equal to about 85 xc3x85, 90 xc3x85 or 95 xc3x85.
Heat treatment may provoke an increase in the TL of the glazing panel. Such an increase in TL may be advantageous in ensuring that TL is sufficiently high for the glazing panel to be used in a vehicle windscreen. TL may increase in absolute terms during heat treatment by, for example, greater than about 2.5%, greater than about 3%, greater than about 5%, greater than about 8% or greater than about 10%.
Examples of the present invention will now be described with reference to FIG. 1 which is a cross-section through a glazing panel prior to a bending and tempering operation (for ease of representation, the relative thicknesses of the glazing panel and coating layers are not shown to scale).